For most known antenna designs the dipole elements are formed to specific lengths to resonate to specific frequencies. Dipoles are usually made up to suit 50 ohm, 75 ohm or 300 ohm impedances. Key measurements within the dipole are harmonics (eg 1, ½, ⅓, ¼) of specific frequency wavelength(s). A 50 ohm dipole is cut to a ¼ wave with an earth screen and a 75 ohm dipole is a balanced dipole made of two ¼ wave dipoles or a folded dipole with a balun. These dipoles are generally tubular. Such dipoles perform acceptably for frequencies close or harmonically related to the frequencies for which they are designed. However, these dipoles perform less acceptably, if at all, for frequencies that are not harmonically related to the frequencies for which they are designed.
Known broadband dipole designs offer very low gain. These dipoles are consequently unusable in some situations. A low gain dipole requires higher signal strength than high gain antennas to perform as reliably as a higher gain dipole. However known methods to increase the gain of a dipole reduce available bandwidth.
Low dipole gain and narrow dipole bandwidth lead to increases in the size of the resulting antenna assemblies. Larger antennas use more materials and are more expensive to manufacture than smaller antennas. They also have the disadvantages of taking more effort to secure and being more visually obtrusive.